1. Field of the Invention
The present invention relates to exhaust devices for a motorcycle engine and in particular to an exhaust device that improves the noise reduction efficiency of a muffler.
2. Description of Background Art
A plurality of exhaust pipes for a multicylinder engine are known wherein the exhaust pipes are collected, and expansion is performed one time in an exhaust chamber; which is then connected to a muffler. Thus, noise is reduced and the size of the muffler is reduced. See, for example, Japanese Patent Publication No. Hei 6-50052.
Increasing a cross-section ratio is known as a method of improving the noise reduction efficiency of a muffler. More specifically, increasing a ratio between a cross section Sa of an inlet passage of the muffler and a passage-sectional area Sb of an expansion chamber, Sb/Sa, can reduce noise accordingly.
On the other hand, even if the exhaust chamber is provided as in the conventional example, the noise reduction efficiency of the muffler itself cannot be improved. The general structure is that the inlet of a cylindrical muffler is provided at the leading end portion of the muffler so as to face a back and forth direction. Such a structure cannot increase the cross-section ratio so much.